The overall goal of Project 2 is to discover anti-cancer drugs based on disrupting receptor tyrosine kinase (RTK) oncogenic signaling. RTK are a family of receptors that play a central role in cell proliferation by binding and transducing growth signals from peptide growth factors such as EGF, FGF, VEGF, heregulin and PDGF at the cell surface to the nucleus. In many human cancers, RTK and/or their ligands are frequently over- expressed. This results in constitutive activation of RTK signaling which has been associated with metastasis, poor prognosis and shortened patient survival. Further support for the involvement of RTK in human oncogenesis comes from the observation that antagonizing RTK signaling, either by anti-RTK specific antibodies or dominant negative forms of RTK ligands, leads to inhibition of human tumor growth in animal models, providing proof of concept and validation for using RTK signaling as a target for discovering novel anti-cancer drugs. The hypothesis to be tested in this proposal is that inhibitors of RTK signaling will be effective anti-cancer drugs against human tumors where RTK signaling is aberrantly activated. The overall goal of Project 2 is to discover novel anti-cancer drugs based on screening several combinatorial libraries for compounds that will selective and potently antagonize RTK oncogenic signaling. This will be accomplished by: (1) identifying lead peptides by screening phage-display peptide libraries for sequences that bind EGFR, FGFR, PDGFR, erbB2, flk-1, or their ligands, EGF, FGF, PDGF, heregulin (erbB2/erbB3 or erbB2/erbB4) and VEGF and to provide such leads to Project 1 for combinatorial peptidomimetic library synthesis. (2) Peptides, peptidomimetics and combinatorial libraries synthesized by Project 1 will be evaluated for their potential to disrupt RTK signaling. Two high throughput assays will be used, one cell-based measuring receptor tyrosine auto-phosphorylation , and the other in vitro measuring tyrosine kinase activity of the receptor. Results from these studies will be used by Project 1 for lead optimization. (3) to establish the selectivity of RTK antagonists using "smart" cell-based assays. Human tumor cells that are known to depend on specific growth factors and/or their receptors for malignant growth will be used to evaluate the ability of RTK signaling antagonists to inhibit growth factor-stimulated DNA synthesis, cell cycle progression, proliferation, malignant transformation, angiogenesis and apoptosis. Transformed NIH3T3 cells that are engineered to over-express EGFR, erbB2, FGFR-1, PDGFRbeta, and flk- 1 will also be used to confirm the selectivity of the RTK signaling antagonists. (4) Promising leads to disrupt RTK oncogenic signaling will then be evaluated for their potential to inhibit tumor growth and angiogenesis in animal models using murine and human tumors where RTK signaling is aberrantly activated. The studies described in Project 2 will lead to the discovery of RTK oncogenic signaling inhibitors with potential as novel anti-cancer drugs, and will ultimately result in broadening the spectrum of human tumors that can be successfully treated.